What does Theresa May know about Islam such that she can decide what is a perversion of it? Precious little, I’d wager. Otherwise, she’d not babble on about “Islamist extremism,” a term right out of the Department of Redundancy Department.

If you are an Islamist in the West, you are, by definition, an extremist. An Islamist is a Muslim who believes Islam requires the imposition of sharia, Islam’s ancient, totalitarian societal system and legal code.

“Islamist” is a term we in the West use in the hope that, because there are Muslims who are tolerant, pro-Western people, it must not be inevitable that Islam itself — or at least some interpretations of Islam — will breed the fundamentalist, literalist, supremacist construction of Islam.

It may be a grave error to adopt this hope, especially since it has been elevated into seemingly incorrigible policy. Does the incontestable existence of moderate Muslim individuals necessarily translate into a coherent, viable doctrine of moderate Islam? Turkey’s President Recep Tayyip Erdogan, to take just one very influential Muslim leader, says no: The West’s invocation of “moderate Islam” is “ugly,” he counters, because “Islam is Islam, and that’s it.” Erdogan is a close ally of the Muslim Brotherhood, the world’s most influential Islamist organization. If he’s right that there’s just one true Islam, rest assured that it’s not friendly to the West. Erdogan describes the Western call for Muslim migrants to assimilate in their new European societies as “a crime against humanity.”

Meanwhile, many students of Islam observe that its aggressiveness, intolerance of non-Muslims, and subjugation of women are indisputably rooted in Islamic scripture. Wherever there is Islam, they maintain, there will inevitably be Islamists; and when those Islamists reach a critical mass of population (which can be considerably less than 50 percent), there will inevitably be sharia activism.

They may be right. I don’t want them to be . . . but hope is not a national-security strategy — even if it has been the West’s national-security strategy for a quarter-century.